Aged or contaminated bank 2 sensor 2 heated oxygen sensor (HO2S) that has slowed its switching rate; Exhaust leaks ahead of the downstream sensor, such as a cracked pipe or failed gasket, that dilute the sample; A failing bank 2 catalytic converter that no longer stores and releases oxygen as designed; Wiring damage or corroded connector pins in the sensor circuit, especially near the exhaust heat path; An engine misfire or rich running condition on bank 2 that has contaminated the sensor over time; Use of leaded fuel, silicone-based sealers, or excessive oil consumption fouling the sensor element; A PCM calibration issue or low system voltage that skews the cross-count logic

DTC codes / GM codes / P1159

P1159 · GMHO2S Cross Counts Bank 2 Sensor 2

Q: What does code P1159 mean?

HO2S Cross Counts Bank 2 Sensor 2. P1159 on GM vehicles indicates that the powertrain control module has detected an abnormal number of voltage cross counts from the downstream heated oxygen sensor on bank 2, which monitors the catalytic converter on the side of the engine that does not contain cylinder number one. The computer expects this sensor's signal to switch states at a predictable rate once the converter is lit off, and a count outside the calibrated window tells the module that the sensor or the exhaust stream it samples is not behaving as designed.

P1159 on GM vehicles indicates that the powertrain control module has detected an abnormal number of voltage cross counts from the downstream heated oxygen sensor on bank 2, which monitors the catalytic converter on the side of the engine that does not contain cylinder number one. The computer expects this sensor's signal to switch states at a predictable rate once the converter is lit off, and a count outside the calibrated window tells the module that the sensor or the exhaust stream it samples is not behaving as designed.

SystemPowertrain

Code typeGM specific

SeverityMedium

Fix difficultyIntermediate

AreaFuel and air metering

Symptoms you may notice

Illuminated check engine light, often with no other symptoms besides the warning light
Slightly rough idle or a subtle stumble that the driver may attribute to bad fuel
A faint sulfur or rotten egg smell from the exhaust when the converter is not trimming properly
Marginal fuel economy loss that becomes noticeable over several tanks of fuel
Intermittent hesitation during light acceleration when the sensor signal is erratic
Failed state emissions inspection because the oxygen monitor has not completed

Common causes, most likely first

Aged or contaminated bank 2 sensor 2 heated oxygen sensor (HO2S) that has slowed its switching rate
Exhaust leaks ahead of the downstream sensor, such as a cracked pipe or failed gasket, that dilute the sample
A failing bank 2 catalytic converter that no longer stores and releases oxygen as designed
Wiring damage or corroded connector pins in the sensor circuit, especially near the exhaust heat path
An engine misfire or rich running condition on bank 2 that has contaminated the sensor over time
Use of leaded fuel, silicone-based sealers, or excessive oil consumption fouling the sensor element
A PCM calibration issue or low system voltage that skews the cross-count logic

How to diagnose and fix it

Connect a scan tool and record freeze-frame data plus the bank 2 sensor 2 voltage trace to confirm the cross-count complaint
Inspect the entire bank 2 exhaust path from the manifold to the downstream sensor for leaks, cracks, and loose clamps
Check the sensor connector and harness for chafing, corrosion, and pushed pins, then measure reference and ground circuits
Graph the upstream and downstream oxygen sensor signals together to judge whether the converter or the sensor is at fault
Perform a propane or smoke test on the intake and exhaust to rule out unmetered air and leaks before condemning parts
Replace the bank 2 sensor 2 heated oxygen sensor with the correct GM-specification part if the signal is lazy or biased
Clear the codes, complete the oxygen monitor drive cycle, and verify that P1159 does not return before releasing the vehicle

Cross counts point to sensor and converter health

Cross counts measure how often the downstream oxygen sensor voltage crosses a midpoint threshold, so a lazy sensor and a worn converter can produce nearly identical P1159 data.
A bank 2 exhaust leak just ahead of the sensor is one of the most commonly missed causes because it pulls in outside air and inflates the cross-count activity.
Technicians who replace the converter first often find the code returns because the original sensor was already contaminated and slow to respond.
Oil or coolant consumption on bank 2 can coat the sensor element and change its switching behavior long before the sensor fails outright.
The code can set from a simple loose sensor connector that intermittently drops the signal, so always wiggle-test the harness while watching live data.

Can I keep driving with P1159?

The vehicle remains safe to drive with P1159 because the fault affects emissions monitoring rather than engine control, but avoid long periods of heavy load or towing until it is diagnosed. If the check engine light begins flashing or drivability worsens, stop driving and have the vehicle inspected promptly.

Tools that help

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Guidance is general and written for GM vehicles. Exact tests and values vary by model, so confirm the fault before replacing parts.